It is known in principle that during CT examinations scattered radiation effects are produced that lead to inaccuracies in the measurement of the absorption of x-radiation. Looking first at this effect in unifocal detector systems, the problem of scattered radiation here becomes larger the wider the beam fan used is expanded, since the sites at which scattered radiation is produced increase correspondingly.
In the case of such CT systems, this known effect is counteracted by fitting in front of the detector so-called scattered radiation collimators that expose in front of each detector element only the direct radiation direction between detector element and focus, and largely shade all the other directions. Such scattered radiation collimators are also used with the bifocal or multifocal detector systems. However, these scattered radiation collimators cannot diminish the scattered radiation that is produced by beams of another focus arranged with an angular offset and has the same spatial orientation as the actual direct beam that originates from a focus opposite the detector and whose intensity is to be measured.
There is thus in principle the problem of determining the fraction of this scattered radiation in the total measured intensity of the radiation, and of correcting the measured radiation intensity by this fraction.
A similar method for scattered radiation correction in a bifocal detector system is disclosed, for example, in patent specification DE 102 32 429 B3. In the case of this patent specification, two focus/detector systems arranged angularly offset from one another are operated in an alternating fashion at least temporarily, such that the scattered radiation actually occurring that originates from the focus/detector system being operated can be measured directly in the focus/detector system respectively not switched on. In order to carry out this method, it is necessary to operate the X-ray sources in an alternating fashion at least partially, as a result of which at these times image information from the CT scan is lacking at least in the detector of the X-ray tube that is not being operated, and so gaps are produced in the data acquisition.
In this variant of the operation, there is the problem that the scanning during the alternating switching on/switching off of the tube or the radiation is not complete and exhibits gaps.